The invention relates to a deceleration sensing valve assembly which operates by sensing the deceleration of a vehicle, and more particularly, to a deceleration sensing valve assembly including a valve body which is adapted to move away from its valve seat under its own inertia whenever the deceleration of the vehicle exceeds a given value.
In conventional deceleration sensing valves, a valve seat is located forwardly of a valve body, as viewed in the direction of movement of the valve body under its inertia. When a given deceleration is obtained by a low liquid brake pressure as when the vehicle is empty, the valve body is caused to move into seating on the valve seat under its inertia, thereby interrupting a flow path to maintain the liquid brake pressure which is introduced to a point downstream of the deceleration sensing valve at a low value. On the other hand, when a given deceleration is not obtained if the liquid brake pressure increases to a high value as when the vehicle is occupied, the valve body is located remote from the valve seat under gravity, permitting the high liquid brake pressure to be introduced into the flow path downstream of the deceleration sensing valve. A deceleration sensing valve of the kind described is used in combination with a proportioning valve which increases the liquid brake pressure introduced into a rear wheel cylinder at a low increase rate relative to the liquid brake pressure introduced into a front wheel cylinder, and normally controls the magnitude of a bias applied to the proportioning valve in accordance with the magnitude of the liquid brake pressure introduced into the flow path downstream of the deceleration sensing valve, in a manner such that the bias is maintained low to enable the proportioning valve to be responsive to a low liquid brake pressure when the vehicle is empty while the bias is increased to enable the proportioning valve to be operable only after a high liquid brake pressure is obtained when the vehicle is occupied, thus assuring braking characteristics which are suitable when the vehicle is empty and loaded, respectively.
However, because of the location of the valve seat forwardly of the valve body as viewed in the direction of movement thereof under inertia and the arrangement that the valve body moves under inertia until its seats on the valve seat, conventional deceleration sensing valves suffer from a disadvantage that in particular when the vehicle is empty, extraneous factor such as oscillations of the vehicle may cause a shift in the timing when the valve body becomes seated. This in turn causes a variation in the liquid brake pressure which is confined in the flow path downstream of the deceleration sensing valve, thus making the empty vehicle characteristic unstable.